Measurement While Drilling (MWD) is now commonly practiced in the petroleum related drilling industry. The most common apparatus used down hole, for signal generation, is the pressure pulse signal generator. Such apparatus periodically alters the resistance to the flow of the mud stream moving down the drill string bore. Resistance change in the mud stream is usually altered by either a mud siren that generates standing pressure waves, or by digital pulsers that open or close signal valves. The known mud sirens signal by briefly changing the siren speed.
The MWD apparatus can be installed in the drill string while the drill string is on the surface or lowered into the drill string after the drill string is suspended in the well bore. If installed after the drill string is in the well, it is referred to as the shuttle system, and the MWD package is called a shuttle package. In either case, the pulser, in use, is installed in the drill string but the use of the term “installed system” usually means the form installed while the drill string is on the surface, and that relationship will be used herein.
The shuttle package usually contains the mechanical pulser, the instrument package, and a battery pack. Use of the shuttle normally requires azimuthal orientation relative to a scribe line on the drill string if control of well bore direction is expected. The orientation matter usually dictates the use of a mule shoe or it's equivalent in the drill string bore.
The installed version of the pulser usually does not use a battery pack, but generates power down hole with a mud driven turbine and attached alternator. Alternators on shuttle packages are not known to be successful.
The installed version can use either negative or positive signal pulses. The negative pulse is normally generated by briefly opening a mud stream by-pass channel to briefly reduce the mud pressure in surface mud circuits. No known negative pulse generating shuttle pulsers are currently in use.
The demand for shuttle package recovery ability is often related to the cost of the instrument package if the drill string becomes stuck and the pulser system is lost. The cost of the instrument package is constantly dropping and that need may diminish. The pulser and the instrument can be made separable and the instrument alone can be recovered. That decrees a pull-apart overall package. There is no need for the pull-apart feature to contribute to reliability questions. The pull-apart would only be exercised if the system faces loss in the hole.
If pulsers could be depended upon to complete a normal bit run before failure, the version that can be installed at the surface should offer the most desirable performance and reliability features.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.